1. Field of the Invention
The present invention relates to a system, method and apparatus for monitoring hydraulic pressure in a fluid filter, and for detecting filter clogging. More particularly, the present invention relates to a system, method and apparatus including a fluid filter assembly which incorporates one or more thick-film pressure sensors.
2. Description of the Background Art
Preserving and maintaining oil quality is important to maximizing the useful life of an internal combustion engine. Similarly, the detection of oil contamination and deterioration, in an internal combustion engine, is important in prolonging the useful life of the engine.
The useful life of motor oil depends on many factors, including engine condition, ambient operating conditions, vehicle usage, vehicle servicing, and type of oil used.
While most car manufacturers recommend changing the engine oil of an automobile at three months or three thousand miles, whichever comes first, many automobile owners and operators fail to regularly change the engine oil of their automobile within the recommended timeframe.
Where deteriorated oil is subject to prolonged use because of infrequent oil changes, the useful life of an automobile engine is greatly reduced.
It is well known that if a fluid filter becomes partially clogged, the hydraulic pressure increases therein, upstream of the clogged filter element, because greater pressure is required to force fluid through the clogged filter.
As a result of the above concerns, some relevant oil pressure monitoring equipment has been developed.
Some electromechanical switches have been developed to sense oil pressure, and to send a signal to an operator when the pressure value, or a pressure differential, exceeds a threshold value. Examples of these pressure-sensing switches may be found in U.S. Pat. Nos. 2,251,648, 2,810,034, 2,879,892, 3,644,915, 3,654,414, and 4,480,160. The switches in the above-cited references normally incorporate a spring-biased diaphragm, or a spring-biased piston, and are generally separate from any associated filters or filter assemblies.
Some oil filter assemblies, incorporating electromechanical pressure sensing switches, have also been developed to monitor oil pressure within the filter, and to send a signal to an operator when the pressure in the filter exceeds a threshold value, indicating that the filter element has become clogged. Examples of oil filter/sensor assemblies may be found in U.S. Pat. Nos. 2,879,892, 4,885,082, 5,569,373 and 5,674,380.
While the known devices have shown some utility for their intended purposes, a need still exists in the fluid monitoring art for an improved pressure-sensing oil filter apparatus including a low-cost pressure sensor. An oil filter assembly that measured a pressure differential between the inlet and outlet zones within a hydraulic oil filter would be particularly beneficial to vehicle owners.
An improved oil filter/sensor assembly is needed that can be serviced or changed by non-expert service personnel or by a vehicle owner or, if desired, when the device wears. In particular, there is a need for an oil filter/sensor assembly incorporating one or more small cost-effective sensors, suitable for high-volume production.
The present invention has been developed to overcome the foregoing limitations and disadvantages of known oil quality sensors, and to generally fulfill a need in the art for an improved oil filter/pressure sensor assembly, which provides cost-effective and ongoing oil quality monitoring.
In accordance with one of the preferred embodiments hereof, the present invention includes an oil quality monitoring system including an oil filter/tapping plate with built-in sensor assembly, a flexible circuit tape connector, a differential amplifier circuit, a radio frequency (RF) transmitter and an antenna.
Accordingly, it is an object of the present invention to provide a method and apparatus for monitoring the condition of an oil filter, through in-situ analysis
In-situ monitoring offers a superior method of detection, as it monitors the actual oil circulated through the engine. However, proper location of the in-situ device is important for accurate monitoring, i.e. the sensor should be located in a spot where oil is actively circulated, rather than in a xe2x80x98dead spotxe2x80x99 (a location with little or no flow). The highest cycling area of engine oil is within or near the oil filter, and accordingly, the present invention incorporates in-situ detection using a sensor which is made part of an oil filter assembly.
Such an in-situ oil monitoring device is advantageous because incorporation of the sensor into an otherwise conventional oil filter permits the inventive system to be retrofitted to any car, rather than limiting application to new cars only. This capability permits vehicle owners of virtually all makes and models to reap the benefits of oil quality monitoring, which preserves life of their vehicles"" engines. Incorporating the sensor into the oil filter also affords a cost-effective method of oil monitoring, as it requires no specifically designated mounting area and no separate maintenance; and a worn sensor is automatically removed and replaced, as part the oil filter assembly, during an oil change.
Another object of the present invention is to provide a flexible polymer thick film (PTF) as a component of the sensor. A printed sensor pattern on a polymer film permits the sensor to conform to the shape of the surface into which it would be integrated, which provides for installation in tight locations or between two fitting surfaces where conventional sensors cannot fit. As a result, the sensor is capable of fitting on a tapping plate of an otherwise conventional oil filter.
Still another object of the present invention is to use multiple pressure sensors implemented as a force-sensitive resistive PTF material, which includes electrically conducting particles suspended in a non-conducting binder material. These binder materials may be polymers, polyesters, silicone or any other non-conductive material; while the semiconductor filler nanoparticles may be carbon black, copper, gold, silica, or any other sufficiently conductive material.
Two matched PTF pressure sensors are, preferably, placed on opposite sides of the filter tapping plate. The location of the PTF sensors provides monitoring of both filter inlet pressure and filter outlet pressure.
Each sensor operates as an electrical resistor element that decreases its bulk resistance when an external force (i.e. fluid pressure) is applied thereto. Applying external force (i.e. fluid pressure) to the PTF causes the conductive particles to move closer together and even to contact each other in some instances, causing the overall electrical resistance to decrease. A decrease in the resistance occurs due to localized increased concentration of the conductive particles in the polymer binder.
Yet another object of the present invention is to include a circuit connector to the sensor element, in which the connector is provided by conductive PTF ink. The circuit connector relays information from the pressure sensors within the PTF to a differential sensing amplifier circuit within an electronic control module, which converts the two single ended output voltages (i.e. the inlet and outlet pressure) into an equivalent differential voltage output.
A further object of the present invention is to include a differential sensing amplifier wherein two dedicated voltage divider circuits ratiometrically convert resistance values for inlet and outlet pressure into equivalent voltage outputs. The inlet pressure signal is conditioned by a voltage follower stage whose output is connected to the positive terminal of the difference amplifier. The outlet pressure signal is also conditioned by a dedicated voltage follower and connected to the negative terminal of the difference amplifier. The difference value (inlet pressure-outlet pressure) is output by the differential amplifier stage to the RF transmitter to be transmitted to the vehicle user.
By way of example, a PTF pressure sensor pattern with an inner diameter of 0.8125 inch, outer diameter of 0.9375 inch, lead attachment spacing of 0.1875 inch, lead attachment length of 0.25 inch, and ink mix ratio factor of 0.15 inch to 1 has an average equivalent of 4.15 megaohms of electrical resistance at 0 pounds per square inch (psi) and 3.6 megaohms of electrical resistance at 60 psi. The sensor output slope value is xe2x88x9229.3xc3x97103 and linearity fit factor (R2) is 0.988. The filter differential pressure range for most passenger vehicles is from 0 to 60 psi.
For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts.